Evaporation & Wort Boiling
IBD/BFBi Midlands Section Engineering Symposium on
Heat Transfer and Refrigeration
Burton-on-Trent – Jan 2014
John Hancock – Briggs of Burton
Evaporation & Wort Boiling - Contents
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Boiling & Evaporation - Basics
Wort Boiling Process
Whisky Distillation Process
Boiling & Condensation Heat Transfer
Heat Transfer – Fouling, ΔT & Surface Area
Wort Boiling Systems
Energy Recovery
Wort Boiling vs Product Quality
Boiling & Evaporation – Phase Change
• Phase Change
– Liquid to Vapour – Energy Intensive
– Specific heat of Evaporation – hfg
• Energy to evaporate 1 kg
• Water - hfg = 2257 kJ/kg at atm pressure
– Boil Energy input
• e.g. 5% volume off 1000 hl
= ME x hfg
ME = Mass Water Evaporated
– ME = 1000 hl x (5/100) x 100 kg/L = 5,000 kg
= 5,000 kg x 2257 kJ/kg = 11,285,000 kJ
=11,285 MJ
Boiling & Evaporation – Energy Intensive
• Energy Intensive
– Boil 5% off 1000 hl
=11,285,000 kJ = 11,285 MJ
– Pre-boil - Heat 1000 hl wort – 75 to 100 °C
= M x CP x (T2 – T1)
Mass M = 1000 hl x 100 kg/L = 100,000 kg
Specific Heat CP kJ/kg K
Energy to heat 1 kg by 1 °C (or °K)
Water = 4.2 kJ/kg K
Wort = 4.0 kJ/kg K
= 100,000 x 4.0 x (100 – 75) = 10,000,000 kJ
= 10,000 MJ
Boiling & Evaporation – Energy Flow
• Boil 5% off 1000 hl
– Heat Input = 11,285,000 kJ
– 60 minute boil
– Q = 11,285,000 / (60 x 60) = 3,134 kW
• Heat 1000 hl wort – 75 to 100 °C
– Heat Input = 10,000,000 KJ
– 50 minutes heating
– Q = 10,000,000 / (50 x 60) = 3,333 kW
Boiling & Evaporation – Steam Flow
• Steam
• Most commonly used heating media for large scale
efficient heating processes
• Condensation –
– Vapour to Liquid
– Reverse of Boiling
• Specific Heat of Condensation – hfg
–
–
–
–
Same as Heat of Evaporation
Energy released on condensing 1 kg
Steam (Water) - hfg = 2133 kJ/kg at 3 bar g
Lower than at atm pressure (2257 kJ/kg)
Boiling & Evaporation – Steam Flow
• Energy in = Energy out
• Boil 5% off 1000 hl
Q = 3,134 kW
Steam Flow = 3,134 kW / 2133 kJ/kgK
= 1.47 kg/s = 5,290 kg/h
Steam Flow similar to Evaporation rate
5,290 kg/h Steam (6% higher) vs 5,000 kg/h Evap
• Heat 1000 hl wort – 75 to 100 °C
Q = 3,333 kW
Steam Flow = 3,333 kW / 2133 kJ/kgK
= 1.56 kg/s = 5,625 kg/h
Wort Boiling Process
• Wort Boiling Objectives
– Why Boil?
– How?
• Process Requirements
• Affect on –
– Downstream processes
– Product quality
• Batch vs Continuous Boiling
• Predominantly a Batch process – high peak loads
• Continuous boiling reduces utility peak loads
Wort Boiling Objectives – Why Boil?
• Flavour Development
– Volatile Removal
– Isomerisation
Water
Heat
• Stabilisation
Mash
Conversion
Water
Hops
Heat
– Sterilisation
– Enzyme Inactivation
• Concentration - Gravity / Volume
Enzymatic Conversion
Mash
Mash
Separation
• Wort Clarity –
– Trub Formation - Flocculation
Malt
Sweet Wort
Wort
Boiling
Filtration
Leaching
Spent grain
Evaporation
Volatile stripping
Hopped Wort
Settling &
Wort
Trub
Clarification
removal
Hot
Trub
wort
Wort
Cooling
Cooling
Cold wort
Achieving Objectives – How?
Objective
Process Factors
Volatile Removal
Evaporation & Turbulence
Isomerisation
Temperature & Time
Flocculation
Vigorous Boil (Wort/vapour interface bubbles), Low Shear
Sterilisation & Enzyme Inactivation
Temperature & Time
Gravity / Volume
Evaporation
Evaporation itself is not the key process in Wort Boiling,
Other factors are more critical.
Whisky Distillation Process
• Malt Whisky Distillation – Pot Stills
–
–
–
–
Wash 8% alcohol
Spirit 60 % alcohol
Water evaporation = large energy input
66% of Distillery energy input
• Two (or 3) stage process
– Wash Stills – major evaporation / energy load
– Spirit Stills
– Batch Distillation – 2 or 3 stage
Whisky Distillation Process
• Evaporation higher as % of feed than wort boiling
– 30 to 40% of initial volume / stage
• Changes through Batch Distillation –
– Wash / Spirit temperature increases
– Alcohol concentration drops
Heat Transfer Coefficients
Boiling & Condensation
Boiling
Condensation
Film Boiling –
• Vapour insulates liquid from
surface
• Vapour conductivity low
• Poor heat transfer
• Rapid fouling
Film Condensation –
• Surface Permanently wet
• Thin liquid film flowing down tubes
• Vertical tubes – Velocity increases down
tube
• Horizontal tubes – Flow from tube to
tube
• Liquid Conductivity high
• Good Heat Transfer
Nucleate Boiling –
• Vapour forms in small bubbles
• Bubbles quickly leave surface
• Increases turbulence
• Good heat Transfer
Dropwise Condensation –
• Surface not wet
• Droplets form
• Quickly run off leaving surface bare
• Very High Heat Transfer Rates
Boiling - Surface & Temperature
• Boiling Mode affected by –
– Temperature Difference
– Surface ‘Wettability’
• Copper
– ‘Wettable’
– Vapour bubbles easily released
– Film boiling only at very high ΔT
• Stainless Steel
– Non-Wettable
– Vapour clings to surface
– Film boiling can occur at low ΔT
Boiling – Heat Transfer Modes
Heat Transfer - Nucleate Boiling
Most commonly used mode for boiling wort.
• Internal Heater
• External Thermosyphon
Vapour Bubbles Beneficial
1) Protein Denaturation & Coagulation
2) Volatile Stripping
3) Hop Acid Isomerisation
Intensity of Boil
The more steam vapour bubbles formed per
unit volume of wort the more intense the boil
Two Phase Flow
( Liquid &
Vapour )
The Difference in
Density Between
Single Phase &
Two Phase is the
Driving Force for
the
Thermosyphon
Single Phase
Flow (Liquid)
Heat Transfer Coefficient & Fouling
L
Heat Transfer - Fouling, Area & ΔT
• Q = U x A x ΔT
– U – Heat Transfer Coefficient
• Higher for Nucleate Boiling
• Low for Film Boiling
• Fouling reduces U progressively
– A – Surface Area
• Low Surface Area needs higher ΔT
– ΔT – Temperature Difference – Driving Force
• Low ΔT needs Large Surface Area
• Low ΔT reduces fouling
Wort Boiling Heat Transfer – Surface Area
Higher surface area lowers heater surface temperature in contact with wort.
Lower Delta T is considered beneficial for foam, flavour & flavour stability
Wort Boiling Heat Transfer - Fouling
Metal
U
U
U
The larger external Heater will reach this degree of fouling after 25 brews, then needing 1.5 Bar steam @ 127 ºC.
The smaller Internal Heater would reach the same degree of fouling after 10 brews. This would require 6.5 Bar
Steam @ 168 ºC, which is not advisable. Normally wort heaters are limited to 4 Bar steam to avoid film boiling
and therefore the small internal heater will require CIP after 5-6 Brews.
Wort Boiling Technology
• Internal Wort Heaters (IWH)
• External Wort Heaters (EWH)
– Pumped
– Thermosyphon
• Kettle-Whirlpools
• Control
• Steam Injection
Internal Wort Heater
• Traditional
– e.g. North America
• Percolators
– Very low Surface area
• Tubular Internal Heater
– Low Surface Area
Spreader
Working level
Wort
Kettle
Fountain
• Typically 0.08 m2/hl
• Needs frequent CIP
• Fountain & Spreader
• May be pump assisted
– Similar to External Heater
Internal
Wort
Heater
Condensate
Steam
Outlet
Internal Wort Heater Technology
EWH – Fountain & Spreader
• Flexible
– Brewlength
– CIP volume
• Fountain & Spreader
• Thermosyphon
Spreader
Working level
Wort
Kettle
Fountain
EWH outlet ~
2 phase flow
– low shear
– Typically 0.2 m2/hl
• Or Forced Circulation
– Pumped
– high shear
External
Wort
Heater
Steam
Condensate
Circulation pump
External Wort Heating Development
EWH – Fountain & Spreader
EWH – Symphony
• Thermosyphon
• Tangential Inlet
– Low Shear
• Boil on the whirl
– Improved Mixing
• 2 Phase flow
– Vapour / Liquid interface
– Volatile Stripping
Tangential Inlet ~
2 phase flow
Working level
Wort
Kettle
External
Wort
Heater
Steam
Condensate
• EWH – High Surface Area
– Vapour bubble formation
Circulation pump
EWH – Symphony
CUB, Yatala - Australia
Twin stream Brewhouse
10 brews / day, 825 hl cold wort
Symphony Wort Boiling and
Energy Recovery systems
EWH
Tangential Inlet
Kettle-Whirlpools
Combined Wort Boiling + Trub Separation
• Forced Circulation
– High Shear
• Thermosyphon
– ‘Symphony Plus’
EWH – Symphony Plus
• Combined Kettle &
Whirlpool
• Thermosyphon
Circulation
• Eliminates Transfer
to Whirlpool
• Reduced shear
• Improved Trub
Separation
EWH – Symphony Plus
Temp. transmitter
Flow control
Constant
steam set
at 3bar
Steam flow
control valve
Condensate
Pump by-pass
Steam
meter
Steam Injection
• Steam Condenses directly into Wort
•
•
No Heater / Fouling
Condensate dilutes wort, offsetting heat input
• Steam Quality
• As steam condenses into wort –
Steam must be of process quality
• Culinary steam
• Filtered
• FDA approved additives
• Stainless Steel steam system (pipework)
Wort Boiling Control
• Energy in = Energy out
• Mass evaporated is
proportional to mass of
steam condensed
• If uncontrolled - fouling
slows heat transfer which
reduces steam mass flow
and reduces evaporation
• Steam control valve
automatically opens to
increase steam
temperature (pressure) to
restore the target rate of
steam condensation.
Steam Flow Meter
Temperature
Transmitter
Steam
Control Valve
Wort Boiling - Energy Minimisation
• Wort Boiling - Major Energy User
• Minimise Evaporation
– Wort Quality
• Energy Recovery –
– MVR
– TVR
– Energy Store
• Wort Pre-heating
Wort Boiling - Energy Minimisation
Wort Boiling - Major Energy User
Historical data for a 10% Boil
without Energy Recovery
Bottling T
20%
Mashing T
14%
Kettle Boil T
20%
Heating &
Other T
14%
Fridge E
10%
Pumps E
8%
Lighting E
2%
Kettle Raise T
12%
Same Data with 4% Boil with Wort
Preheating using Energy Recovery
Heating &
Other T
14%
Bottling T
25%
Fridge E
13%
Pumps E
10%
Mashing T
18%
Kettle Boil T
10%
Kettle
Raise T
5%
Lighting E
2%
Wort Boiling – Reduce Evaporation
• 1 % reduction in evaporation
– saves approximately 2 to 4% of Brewhouse energy
consumption
– (1 to 2% of total brewery energy consumption)
– and reduces emissions
• Improved kettle utilisation –
– reduced wort heater CIP frequency
• Easy to implement on existing wort kettles
• Dependent on recipe there is a point at which
reduced evaporation will change beer character
MVR – Mechanical Vapour Compression
MECHANICAL
VAPOUR COMPRESSOR
VALVE
VAPOUR 100ºC
COMPRESSED
VAPOUR 120ºC
VAPOUR
EWH
KETTLE
MVR – Mechanical Vapour Compression
• Direct Recycling of Boil Energy
– Minimal Thermal Boil Energy Requirement
• Replaced with smaller Electrical Power Input
– Electricity Requirement 0.1 - 0.7 kWh/hl
• High Capital Investment
– Long Payback Period (>3 years)
• Large rotating machine – Maintenance
• Difficult to Maintain Air Free Wort Boiling
• Contaminated condensed vapour limits reuse
TVR – Thermal Vapour Compression
VENT
VAPOUR
MOTIVE STEAM
7 - 24 bar a
VALVE
STEAM JET VAPOUR
COMPRESSOR
VAPOUR
EWH
KETTLE
MIXED
VAPOURS & STEAM
1.2 – 1.7 bar a
(0.2 to 0.7 bar g)
CONDENSATE
TVR – Thermal Vapour Compression
• Lower Capital cost than MVR
• Recycles 50% or less of boil thermal energy
– Reduced Energy saving
– Can be combined with Energy Store to increase
recovery
• Dual system – increased complexity & cost
• Requires high pressure steam for recompression
– typically 10 bar g or higher
• Contaminated condensed vapour limits reuse
Energy Store – Wort Pre-heating
97⁰
97⁰C
97⁰
97⁰C
97⁰
97⁰C
Underback
80⁰
80⁰C
80⁰
80⁰C
Mash Filter
80⁰
80⁰C
Energy Store, Condenser & Pre-heater
Energy Store Tank
Condenser
Pre-heater
Energy Store – Wort Pre-heating
• 68% to 80% of Wort Heating Energy saved by using
recovered boil energy
• Minimum 3.6% evaporation to recover enough heat for
Wort Preheating.
– Where evaporation exceeds this, excess recovered energy may be
used for CIP or water heating
• Moderate cost
• Simple system with few moving parts
and no high pressure / temperature
• Pre-run & energy store tank required
• Reduces Wort Boiling fouling & CIP
Energy Store – Wort Pre-heating
Energy Reduction
• Heating Energy = M x CP x (T2 – T1)
• No Energy Recovery
– Heat 1000 hl wort – 75 to 100 °C
= 100,000 x 4.0 x (100 – 75) = 10,000,000 kJ
= 10,000 MJ
• With Wort Pre-heating to 92 °C
– Heat 1000 hl wort – 92 to 100 °C
= 100,000 x 4.0 x (100 – 92) = 3,200,000 kJ
= 3,200 MJ
• Energy Saving = 10,000 MJ - 3,200 MJ = 6,800 MJ
= 68% reduction
Steam Saving = 6,800,000 kJ / 2,133 kJ/kg = 3,188 kg/brew
Wort Boiling Systems & Wort Quality
• Wort Boiling System Design Considerations
– Boiling - Evaporation Heat Transfer
– Wort Quality
• Volatile stripping
• Trub
• Stability / foam
• Wort Quality
– Affect of agitation / shear on hot & cold break
– Wort Quality vs Evaporation & Heater Area
– Comparative results
Hot Break & Cold Break vs Agitation
Hot Break
Cold Break
• A vigorous well mixed boil enhances trub formation
• Excessive shear breaks up hot break (trub)
• Creating more cold break
• Filtration problems downstream
Increase in Anti Radical Potential - DPPH
700
Old Brewhse
New Brewhse
600
500
400
300
200
100
0
Start Kettle Boil
End Kettle Boil
Wort Cool Start
Wort Cool Middle
830 hl 6.5%/h x 70 min boil •
•
Existing Internal Heater
New Symphony EWH System (boil on whirl) 0.22 m2/hl
Wort Cool End
Reduction in Furfural levels
1600
Old Brewhse
New Brewhse
1400
1200
1000
800
600
400
200
0
Start Kettle Boil
830 hl 6.5%/h x 70 min boil •
•
Existing Internal Heater
New Symphony EWH System (boil on whirl) 0.22 m2/hl
End Kettle Boil
PBN (Lag Time - min)
ESR Lag Time
100
80
60
40
20
0
EOF
Early
Storage
Old Brewhouse
Late Storage
BBT
New Brewhouse
830 hl 6.5%/h x 70 min boil •
•
PACK
Existing Internal Heater
New Symphony EWH System (boil on whirl) 0.22 m2/hl
A - ESR T150
T150 (Intensity Level)
12.0
10.0
8.0
6.0
4.0
2.0
0.0
EOF
Early Storage
Old Brewhouse
Late Storage
New Brewhouse
830 hl 6.5%/h x 70 min boil •
•
BBT
Existing Internal Heater
New Symphony EWH System (boil on whirl) 0.22 m2/hl
PACK
Evaporation & Wort Boiling